1. Field of the Invention
The invention relates to the use of a pulse oximetry sensor device during birth.
2. Description of the Related Art
A pulse oximetry sensor device for obstetric use is known for example, from DE 43 04 693. Such a sensor device is applied during birth on the leading part of the fetus. The sensor device includes a light emitter and a receiver. The light emitter sends a wavelength that radiates through the tissue of the fetus and is then picked up at least in part by the receiver. At the same time, the EKG of the fetus is measured. In order to be able to draw conclusions about the status of the fetus during birth, the signal occurring during a heart beat between diastole and systole is measured by the receiver. This measurement utilizes the absorption change caused by the arterial inflow of the blood as an indicator for the current fetal status.
During birth, a midwife needs additional information about the labor activity of the birthing mother. Data about the duration, starting time, peak, and end of a contraction are needed. If a midwife determines irregularities, this may be an indication of complications, so that the midwife must call in a physician who will induce further examination.
The use of intrauterine pressure catheters for measuring the labor activity is known. These pressure catheters are placed as a fixation device for standard pulse oximetry sensors between the uterus and fetus and are anchored there by an increase in volume. The catheter's balloon is used for measuring the intrauterine pressure by conducting the pressure to the outside via a tube and measuring the change in pressure at the tube connection. A disadvantage that may occur in the process is that the tube is clamped off during a contraction, so that differential signals can no longer be transmitted.
There is also a risk that germs are introduced into the uterus when inserting the catheter.
The present invention is based on the task of creating a process for recording the maternal labor activity that supplies reliable signals so that a midwife receives measuring values with clear meanings.
According to the present invention, this task is realized by using a pulse oximetry sensor device to measure the change in the oxygen content in the fetal blood during birth. The pulse oximetry sensor device is provided with at least one light emitter and one receiver, connector with an analyzing device, and attached on the leading part of the fetus for measuring the maternal labor activity.
The invention thus uses pulse oximetry in order to obtain information about the maternal labor activity. While in the past pulse oximetry has been used exclusively for monitoring the fetal status via pulse-synchronous pulse oximetry signals, experts were not able to recognize that pulse oximetry also can be used to obtain information about the status of the parturient.
If the pulse oximetry sensor device is attached, for example, to the scalp of the fetus located inside the opening of the cervical os, the blood volume in this part of the scalp rises during a contraction. The pressure between the cervical os and the fetal scalp is so high during a contraction that the venous backflow of the fetal blood is hindered, but is not sufficient to suppress the arterial inflow. The greater blood volume causes greater light absorption and a change in the sensor signal.
If the sensor device is located below the cervical os within the cervix, the opposite effect may occur. The fetal blood is pushed from the fetal tissue during a contraction, so that the light absorption measured by the sensor device decreases.
Thus, reliable signals about the maternal labor activity are always received. Good signals are even received if the fetus changes position during birth.
In a preferred method, the pulse oximetry sensor device can also be used to measure the fetal EKG. In this way, information about the fetal blood flow characteristics during contractions can be gained simultaneously. It is, for example, possible to display the fetal pulse-dependent or pulse-synchronous pulse oximetry signals in a first track, and the pulse oximetry signals for the mother's contractions in a second track.
According to another preferred method, the light emitter is able to output at least one wavelength at which the absorption of the oxygen-rich and oxygen-poor hemoglobin in the fetal blood is approximately equal. This essentially suppresses a signal change as a result of a change in the blood oxygen content. The point at which the absorption of the oxygen-rich hemoglobin (oxyhemoglobin) and oxygen-poor hemoglobin (deshemoglobin) are equal, is also called the isosbestic point.
In a variation of the invention, at least one wavelength emitted by the light emitter is approximately 805 nm. This wavelength is in the range of the isosbestic point. It makes it possible to obtain particularly clear and reliable signals.
In regard to the various types of hemoglobin with unique absorption spectra present in the blood, it is particularly beneficial if a wavelength is emitted at which the greatest possible number of hemoglobin types have the same absorption, or at which the absorption losses are as close together as possible.